Hydraulic systems are used in the operation of many pieces of equipment ranging from position changing systems for such relatively small items as power lifts and apple pickers through blade positioners for mowing machines, rail positioners for automobile transports and gear systems for large motive equipment to gear systems and auxiliary equipment positioners on giant logging machines and earth movers.
Much of the equipment using hydraulic assistance is operated in areas in which an undetected leak of hydraulic fluid can cause major damage, such as that which can be done by hydraulic machinery to the greens or by fairways of a golf course or the fluid leaked from a logging machine to a wilderness logging area.
Systems that have been proposed for detecting leaks in hydraulic systems have been dependent on determining liquid level or determining an operating pressure within the system. The system set out in U.S. Pat. No. 4,119,016 monitors the level of fluid in a hydraulic reservoir and automatically diverts fluid output from the pump outlet to the pump inlet in the event of a drop in liquid level below a predetermined level. In the system of U.S. Pat. No. 4,591,837 a drop of hydraulic fluid liquid level below a predetermined level in either the hydraulic fluid reservoir or an expansion chamber activates an alarm. The system described in U.S. Pat. No. 5,187,973 compares the pressure in a hydraulic conduit to a predetermined minimum allowable pressure so that even small leaks can be detected.